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Re: [dinosaur] Indian titanosaurs (was Re: How many end-Cretaceous dinosaur genera were there)



John D'Angelo <assuming.dinosaur@gmail.com> wrote:

> Some papers, such as Wilson et al. (2011)
> (doi:10.1111/j.1475-4983.2011.01087.x) have said that only two species of
> titanosaur are currently supported for the Indian subcontinent, which was
> the basis of my statement.


Yep, fair enough - no arguments there.  As it stands, there are only
two valid species of Indo-Pakistani titanosaur.  One is _Isisaurus
colberti_.  The second is named either _Titanosaurus indicus_ or
_Jainosaurus septentrionalis_.


> What makes you say that T. indicus and J. septentrionalis have similar
> caudals? The Chhota Simla Jainosaurus specimen preserves a caudal that lacks
> a ventral longitudinal hollow and isn't mediolaterally compressed at all,
> nor is it strongly waisted, which doesn't seem very much like the
> Titanosaurus indicus type specimen. There's less on the Jainosaurus type
> series caudal, but its centrum doesn't seem to be mediolaterally compressed
> and seems to have straight, not convex, lateral margins in anterior
> view--similar to the Chhota Simla Jainosaurus but not T. indicus.


There are five caudals known from the 'Sauropod bed'/Bara Simla site.
Two comprise the type material for _Titanosaurus indicus_, originally
described by Falconer (1868) and named by Lydekker (1877).  Three
further caudals were described by Huene and Matley (1933), who
referred two of these caudals (K20/315 and /316) to _T. indicus_, and
stated "they are possibly the next vertebrae of the same individual"
as the _T. indicus_ type.  The type _T. indicus_ caudals, as well as
K20/315 and 316, all come from the middle third of the tail.  K20/315
and K20/316 agree very closely to the type caudals in size and
morphology: mediolaterally compressed centra with planar surfaces
("flat-sided").  A larger caudal (K20/317) was referred by Huene and
Matley (1933) to _A. septentrionalis_, and comes from a more anterior
(proximal) part of the tail.  K20/317 is certainly less transversely
compressed than the mid-caudals, but the centrum is still fairly
"flat-sided" (as noted by McIntosh [1990] and Jain and Bandhyopadhay
[1997]).

Regarding the 'Sauropod bed'/Bara Simla titansoaur material, Wilson
and Upchurch (2003) note that "It is possible that only one individual
was present, as originally suggested by Matley (1921)".. but "there is
simply no positive evidence supporting this hypothesis."  In fact,
Huene and Matley (1933) actually state “… from their mode of
occurrence, the first impression was that the majority of them
[sauropod bones] belonged to a single individual... but further study
has shown that at least three individuals belonging to more than one
genus, are represented."  This "further study" was Huene’s
idiosyncratic approach to species taxonomy.  Alas, there are no field
records of the 'Sauroped bed' at Bara Simla.

I agree that the Chhota Simla _Jainosaurus_ mid-tail caudal is indeed
quite different to the type _T. indicus_ caudals, which are extremely
constricted and bear a prominent ventral furrow.  But there are
similarities; in the Chhota Simla _Jainosaurus_ caudal "The lateral
surfaces of the centrum are almost planar" (Wilson et al., 2011).  The
Chhota Simla _Jainosaurus_ is a younger individual than the Bara Simla
material, so there might be ontogenetic differences.  Also, the Chhota
Simla titanosaur is referred to _Jainosaurus_ based solely on shared
diagnostic characters in the humerus; certain "minor morphological
differences", along with size and ontogenetic age, mean that the
referral to the material to _Jainosaurus_ is qualified (_Jainosaurus_
cf. _septentrionalis_).


> Is Laplatasaurus madagascariensis from India a different nomen from
> Titanosaurus madagascariensis Deperet 1896?


No, it's the same - my apologies for not being clearer.  Huene (1929)
referred the Lameta (Pisdura) material to _Laplatasaurus
madagascariensis_.


> Regardless, it's part of the
> mid-caudal nightmare so I'm not sure what to make of it. A few complete
> tails from the Lameta beds would be nice.


Yes, a complete (or near-complete) caudal series from the Lameta beds
would be nice - especially if it included vertebrae that match the
original _T. indicus_ type. It would certainly help to resolve this
titanosaur "mid-caudal nightmare" (apt choice of words).  Hopefully
further excavations will be productive in this respect.